Modulation system



June 25, 1940. J. FINCH 2,205,880

MODULATION SYSTEM Original Filed Feb. 27, 1933 SOURCE OF 8 L040 CIRCUIT osc/zur/ous 7J2 A 2 7'0 AMPL lF/ER 4N0 0R FREQUENCY O SOURCE 0 I B 29 Ml/LT/PUER AND OR UMITER AND OR use/Luna: LOAD mac? SOURCE. OF OSC/L LA T/O/VS INVENTOR JAMES L. F/NCH ATTORNEY Patented June 25, 1940 UITED STATES PATET ()FFICi'f.

MODULATION SYSTEM JamcsL. Finch, Patchogue, N. r, assignor to Radio Corporation of America, a corporation of Delaware Application January 15, 1936, Serial No. 59,214, which is a division of application Serial No. 658,735, February 27, 1933, now Patent No. 2,031,639, dated February 25, 1936. Divided and this application August 6, 1937, Serial No.

, 14 Claims.

This application is a division of my United States application #59314 filed January 15, 1936,

Patent No. 2,165,844, July 11, 1939, the latter application being a division of my United States application Serial No. 658,735, filed February '27, 1933, Patent No. 2,031,639 dated February 25, 1936 and concerns a system of modulation that may be applied to a wide variety of uses, such as for the control of a system of power generation or transference in respect to its intensity, phase, frequency, or other properties. The invention is particularly applicable to modulation of high frequency oscillations in any of their characteristics at signal frequency. It may also be applied to the J control of light or heat or fluid streams or of point earlier in the system so as to produce a degenerative effect. The control element in the detector permits the degenerative effect to go to a definite point which is determined by the control' element, but no further than said point. The definite point is adjustable. Thus the system is changed or modulated in accordance with the control element in the detector.

In the prior art it has been the practice to produce modulation bymeans of some control element and to design the system to given linear response to this control element and to suppress any other factors which tend to produce extraneous modulation. Due to the difliculties encountered the resulting modulation is frequently distorted and different from that desired. My invention makes unnecessary these precautions, which are normally expensive and diiilcult to accomplish.

The novel features of my invention have been pointed out with particularity in the claims appended hereto. The nature of my invention and the operation thereof will be best understood from the. detailed description thereof, which follows, and therefrom when read in connection with the attached drawing, in which;

(Cl. l79171.5)

Figure 1= shows a radio transmitter including my novel oscillation relaying device and my novel control means which determine the character of the oscillations being relayed. In this arrangement, energy is derived from the output of a high frequency amplifier connected to a modulator, impressed on a modulation frequency amplifier, and acts therein to control the character of the modulating potentials applied by way of coupling tubes from the modulation frequency amplifier to an electrode in the modulator stage to control the same. I

Figures ,2 and 3 inclusive show modifications of the arrangement of Figure 1. In the modifications of Figures 2 and 3, the controlled modulation frequency amplifier is of the screen grid type and the screen grid and control grids are respectively capacitively and inductively coupled to the output of the amplifier stage. The remaining grid-like electrodes in each of the controlled modulation frequency amplifier tubes are connected to'the source of modulated potentials. I will describe specific embodiments of my invention as applied to the amplitude modulation of a' radio transmitter. It will be understood, however, that the invention is readily applicable to other types of modulation.

Referring to Figure 1 of the drawing, A is the final stage of a transmitter. The final stage A is excited by stage B. The stage B comprises a pair of thermionic tubes I 8 and I9 having the control grids I8 and I9 connected to the opposite terminals of a winding 2|, the center point of which may be connected, as shown, to the pole of a biasing source, not shown, at C. The in-. ductance 2I may be coupled by way of circuit 20 to any source of high frequency oscillations I. The oscillations impressed from I5 on 2| are repeatedand amplified in the tubes I8 and I9 and appear in the inductance 24 connected between the anodes of tubes I8 and I9. The oscillations appearing in 24 are applied to the control grids 32' and 33' of tubes 32 and 33 by way of coupling and blocking condensers 25 and 26. Biasing potential for the grids 32'. and 33' of tubes and 33 is supplied from C connected to a source, not shown, by way of choking coils 29 and 30 respectively. The high frequency oscillations impressed on the control grids of the power amplifler tubes in stage A are repeated and amplified in said tubes and appear in the inductance 34 connected between their anodes. The amplified oscillations may be supplied from the inductance 34 in any manner to a load circuit. For example, the energy may be fed to the load circuit through coupling condensers 35 and 36 in lines 31 and 38 tapped to inductance 34.

l is a three element tube which serves as the detector variably coupled, by way of an inductance '50 connected to its anode t, to the output of the final stage A and responsive to'the amplitude of the output of said stage. The voltage on control grid 2 is made responsive to the voice currents in microphone 3 by means of transformer t and bias battery 5. When the voltage impressed on anode 6, due to the output of A, is high enough to overcome the efiect of the blocking voltage on 2, anode current will flow in tube 9, the direct current component returning through resistor l and the alternating current component through smoothing capacitor 8. Inductance at also prevents the radio frequency anode potential, transferred to 6 from the finalstage-of A, from being short-circuited by t. The control grid it of amplifier tube H has a potential impressed on it due to the resistance drop of the current flowing through I. This amplifier tube ii is resistance coupled to the control grid 62' of modulator tube i2 by means of resistor i3 and bias battery iii. The modulator tube 62 has its anode electrode it" connected to its cathode by way of resistance ii and a. source of direct current voltage not shown. The screen grid electrodes S and S of tubes i 8 and i9 are connected, as shown, to the resistance i'i. A change of current intensity fiowing in resistance ill causes a change in the potential applied to the screen grids of tubes it and it. As the current through i'ldecreases, the potential on the screen grid electrodes 58' and 19 increases and vice versa. In this manner, the tube i2 modulates the screen grids of tubes it and it in the radio frequency amplifier stage B.

The proportions of these circuits are so chosen that when the peak radio frequency potential on t exceeds the cut-off voltage as determined by the voltage on 2 by an appreciable amount, the reaction back through the modulator tube it will reduce the amplitude of the oscillations supplied by stage B to stage Ajand the power output of A until the peak radio frequency potential on 6 just barely exceeds the cut-off voltage. Thus, as the potential on grid 2 is varied in accordance with the voice, the cut-off voltage of i is varied in proportion and the peak radio frequency potential output is automatically adjusted to just exceed this voltage. Thus, the output voltage is modulated truly in accordance with the modulating potentials.

Now, if some extraneous modulation is introduced, such as a hum modulation on the output of radio frequency source E5, or if the gain of stage A or B is varied by reason. of alternating current on the filaments, or .due to inconstant need not have a linear characteristic since any distortion introduced from this cause is of a secondary order.

The filament of the modulator i2 is shown at a negative potential with reference to the filaments of the modulated stage B. This is necessary in order to fully modulate the stage B through the radio transmitter using voice control and amplitude modulation is as follows:

' Starting with no modulation, grid 2 will assume a potential at the middle of its operating range. Assume also that momentarily tube i2 is blocked, thus allowing stage B to pass a maximum amount of power on to stage A. Stage A will in turn put out a maximum power and coincidently will induce a maximum radio frequency voltage on t. This causes a direct current potential to be impressed on i of a value much in excess of that required when acting through amplifier i i and modulator if to decrease the output of B to zero, but when this output has dropped to a value low enough for the voltage on the output of A to have dropped to half value, the voltage on 6 will have dropped to a value just suficient for-the peaks to exceed cut-ofi and thus a stable ccndi tion at this voltage is maintained. Now, assume the voice causes 2 to drop to the most negative output voltage will follow in inverse proportion A any voltage impressed on 2 and thus will follow the voice currents. I

It will be understood that the arrangement shown in Figure 1 may be modified in various manners without departing from the scope of the present invention.

The modulation frequency relay i may be a triode as shown in the preceding circuits, or may be of the screen grid type as shown in Fig. 2. When a tube of the screen grid type, such as tube $6, is used the anode is connected by way of a charging source ti to the terminal of the resistance i. The resistance 7 is connected to the control grid it of amplifier it through a second source 56. The inductance 3 is capacitively coupled to the screen grid electrode 66' of tube E i. Charging potential for the screen grid electrode t l of tube at is supplied by way of a choke 62 and a source of potential 63, a terminal of which is grounded, as is the cathode of tube 64. When the radio frequency voltage induced on the screen grid 84' of 64 has attained the maximum positive value, it is assumed that the tube 64 will-pass plate current then, and then only. This plate current reacts through the succeeding amplifiers ii, i2, etc., as explained before, to prevent the radio frequency voltage appearing in 34 from exceeding acritical value. This particular criti cal value changes with the control grid voltage on the control grid of tube 64. In this way, modulation of the oscillations relayed in the stages A and B which is truly characteristic of the signal is accomplished. This tube 64 may be utilized to replace the tube i in'the prior modification. i

In some cases, it may be desirable to use a tube of the screen grid type as a control tube and apply the modulating potentials to the screen grid and the control potentials to the control grid. In this case, a circuit as shown in Fig. 3 may be used. Here, as in the prior case, the anode of the tube Bl is supplied with positive potential by a source GI and the terminal of resistance 1 is connected to the control grid in of tube l I through a second source 56. Here, however, the control potentials are applied on the control grid Cg of tube 54, which is maintained at a negative potential with respect to the cathode by a battery 63 connected to the choking inductance 62. It is noted that the battery here has its terminals reversed with respect to the battery 63 of Fig. 2. The modulation potentials are applied'to the screen grid electrode 64' from the secondary winding of transformer 4. It is noted here that the battery 5, connected with the secondary winding of transformer 4, has its potential reversed with respect to the battery 5 in the preceding figures. This is in order that a positive potential may be supplied to the screen grid to enhance the amplification characteristics of this tube.

I claim:

1. In a signalling system, a thermionic amplifier tube having its input electrodes coupled to a source of high frequency oscillations, said amplifier tube having a screen grid electrode and having output electrodes coupled in an alternating current output circuit, a second amplifier tube having its input electrodes coupled to the alternating current circuit coupled to the output electrodes of said first named amplifier tube, a

source of modulating potentials, a third am-- plifier tube having a plurality of electrodes,

means coupling one of said third tube electrodes to said source of modulating potentials, means coupling another of said third tube electrodes to the screen grid electrode in said first named am-' plifier tube, and means coupling a third electrode of said third named amplifier tube to an said first named tube, a sou-roe of modulating potentials, a control tube having its input electrodes coupled to said source of modulating potentials and its output electrodes coupled to the input electrodes of a second amplifier tube, said control tube having an auxiliary electrode, a resistance connected between the output electrodes of said second named amplifier tube, a third amplifier tube coupling a point on said resistance to an electrode-in said first named tube, and an inductive coupling between the output electrodes of said first named amplifier and said auxiliary electrode in said control tube.

3. In a signalling system, a thermionic tube having input and output electrodes and having its input electrodes coupled to a source of high frequency oscillations, an amplifier tube having input electrodes coupledto the output electrodes of said first named tube, said amplifier tube having output electrodes, asource of modulating potentials, a control tube of the screen grid type having input electrodes coupled to said source of modulating potentials and having output electrodes coupled to an electrode in said first named tube, and a coupling between an output electrode in said amplifier tube and the screen grid electrode in said control tube.

4. A signalling system comprising, a thermionic tube having input electrodes coupled to a source of oscillations said tube having output electrodes, an amplifier tube having input electrodes coupled to the output electrodes of said first named tube said amplifier tube having output electrodes, a source of modulating potentials, a control tube of the screen grid type having its screen grid coupled to said source of modulating potentials and having output electrodes coupled to the electrodes in said first named tube, and a coupling between an output electrode of said amplifier tube and the control grid electrode in said control tube.

5. In a signalling system for linearly modulating high frequency modulations in accordance with signal potentials, a pair of thermionic tubes each having input and output electrodes and a scr en-like electrode, an alternating current circuit connected between said input electrodes, said circuit being adapted to be energized by high frequency oscillations to be modulated, a second pair of thermionic tubes having input and output electrodes, symmetrical circuits connecting the input electrodes of said second named pair of tubes to the output electrodes of said first named pair of tubes, an alternating current circuit including an inductance connected between the output electrodes of said second named pair of tubes, a modulation frequency amplifier tube of the multi-grid type having an input circuit including one of said grids adapted to be energized by modulating frequency potentials, said modulation frequency amplifier tube having output electrodes connected in a circuit includin a resistance, a coupling between another of said grids of said modulation frequency amplifier and said alternating current circuit connected between the output electrodes of said last named pair of tubes, a thermionic coupling tube having its input electrodes coupled tosaid resistance, a second thermionic coupling tube having its input electrodes coupled to the output electrodes of said first named coupling tube, and a circuit coupling the output electrodes of said second named coupling tube to the screen-like electrodes in said first named pair of tubes.

6. In a signalling system for linearly modulating high frequency modulations in accordance with signal potentials, a pair of thermionic modulator tubes each having a control electrode and an anode electrode, an alternating current circuit connected between said control electrodes, 2. pair of thermionic amplifier tubes each having input and output electrodes, symmetrical circuits connecting the inputelectrodes of said second named pair of tubes to the anode electrodes of said first named pair of tubes, an alternating current circuit including aninductance connected between the anode electrodes of said second named pair of tubes, a modulation frequency amplifier tube having input electrodes adapted to be energized by modulating frequency potentials, said modulation frequency amplifier tube having a screen-like electrode and having output electrodes connected in a circuit including resistance, a coupling between the screen-like electrode in said modulation frequency amplifier tube and the alternating current circuit connected between the anode electrodes of said second named pair of tubes, a thermionic coupling tube having its input electrodes coupled to said circuit including resistance, and a circuit coupling the output electrodes of said thermionic coupling tube to like electrodes in said first named pair of tubes.

'7. In a system for linearly modulating high frequency oscillations in accordance with signal potentials, a thermionic modulator tube having coupled to an alternating current circuit, a second thermionic amplifier tube having a control grid, a cathode, an anode and a screen-like electrode, a circuit coupled between the screen-like electrode and cathode of said second thermionic amplifier tube, said last named circuit being adapted to be energized by the signal potentials, a coupling between the control grid of said second named amplifier tube and the alternating current circuit coupled to the output electrodes of said first named amplifier tube, a resistance connected between the output electrodes of said second named amplifier tube, and a circuit coupling said resistance to an electrode in said modulator tube.

8. In a signalling system, a carrier wave amplifying tube having a control grid-and a cathode,

energized. by waves of carrier frequency, said tube also having an anode connected in an alterhating current output circuit, means connected with an electrode of said tube and with said alternating current output circuit for lowering the gain of said tube when said output energy exceeds predetermined peak values, said means comprising an additional electron discharge tube having an output electrode coupled to an electrode in said tube and a pair of grid electrodes one of which is coupled to said alternating current output circuit, and means for controlling said peak values at signal frequency comprising a source of signalling potentials coupled with said other grid electrode of said additional tube.

9. In a signalling system a carrier wave amplifying tube having a control grid and a cathode energized by waves of carrier frequency, said tube also having an anode connected in an alternating current output circuit, means connected with an electrode at said tube and with said output alternating current circuit for lowering the gain of said tube when said output energy exceeds predetermined peak values, said means comprising an additional electron discharge tube having an output electrode coupled to an electrode in said tube, a control grid, and an auxiliary grld'electrode, a circuit coupling said auxiliary electrode to said alternating cur- .rent output circuit and means for controlling said peak values atsignal frequency comprising a source of signalling potentials coupled with said ing the gain-of said tube when said output energy grid to said alternating current output circuit,

and means for controlling said peak values at signal frequency comprising a source of signalling potentials coupled with said auxiliary grid electrode.

11. In a signalling system, a carrier wave amplifying tube having a screen grid, a cathode, a control grid, and an output electrode, means for impressing carrier waves to be amplified on said control grid and cathode, an additional tube hav ing input electrodes coupled to the output electrodes of said first named tube and having an anode connected in an alternating current output circuit, means connected with the screen grid electrode of said first named tube and with said alternating current output circuit for lowering the gain of said first tube when wave energy in said output circuit exceeds predetermined peak values, said means comprising a third electron discharge tube having an electrode coupled to the screen grid electrode in said first named tube, and a plurality of electrodes one of which is coupled to said alternating current output circuit, and means for controlling said peak values at signal frequency comprising a source of signalling potentials coupled with another electrode of said third tube.

12. In a signalling system, a carrier wave amplifying tube having a control grid, a cathode, and an output electrode, means for impressing carrier wave energy tobe amplified on said control grid and cathode, an additional tube having input electrodes coupled to the output electrodes of said first tube and having an anode connected in an alternating current circuit, means connected withan electrode of said first tube and with said alternating current output circuit for lowering the gain of said first tube when energy in said output circuit exceeds predetermined peak values, said means comprising a third elec- 7 tron discharge tube having an electrode coupled to an electrode in said first tube and having a plurality of grid electrodes one of which is coupled tosaid alternating current output circuit,

and means for controlling said peak values at signal frequency comprising a source of signalling potentials coupled with said other grid electrode of said third tube.

13. In a signalling system, a carrier wave amplifying tube having a screen grid, a cathode, a

control grid, and an output electrode, means for impressing carrier waves to be amplified on said control grid and cathode, an additional tube having input electrodes coupled to the output electrodes of said first tube and having an anode connected in an alternating current output circuit, means connected with the screen grid electrode ofsaid first tube and with said alternating current output circuit for lowering the gain of said first tube when energy in said output circuit exceeds predetermined peak values, said means comprising a third electron discharge tube having an output electrode coupled to the screen grid electrode in said first tube and having a screen grid electrode coupled to said alternating current output circuit, said third tube also having a control grid, and means for controlling said peak values at signal frequency comprising a source of signalling potentials coupled with said control grid of said third tube.

14. In a signalling system, a carrier wave amplifying tube having a screen grid, a cathode, a control grid, and an output electrode,-means for impressing carrier waves to be amplified on said control grid and cathode, an additional tube having input electrodes coupled to the output electrodes of said first tube and having an anode connectedin an alterating current output circult, means connected with the screen grid electrode of said first tube and with said alternating current output circuit for lowering the gain of said first tube when energy in said output circuit exceeds predetermined peak values, said means comprising a third electron discharge device having an output electrode coupled to the screen grid electrode in said first tube and a control grid electrode coupled to said alternating current output circuit, said third tube also having an additional grid electrode, and means for controlling said peak values at signal frequency comprising a sourceof signalling potentials coupled with said additional grid electrode of said third tube. a

JAWS L. MCI-l. 

